The brakes and rotors are designed to wear together. If you need both brakes and rotors front and back and are still under maintenance warranty (36K), which you are buy the BMW Ultimate Care+ which will cover the brakes and let the dealer change them.
I normally change my own brakes, but I did this with my X4 b/c the $700 (at the time) was less than the cost of parts.
https://bmwusaservice.com/ultimatecare